Japanese authorities have so far not proved assertions that Tamiflu causes neurological disorders but will keep a ban on the drug for teenagers as a precaution, the health ministry said Wednesday.
Tamiflu is prescribed for the common flu and has been stockpiled in some countries as a frontline drug in the event of a bird flu pandemic.
But Japanese authorities voiced alarm after more than 100 people who took Tamiflu, mostly young children and teenagers, behaved abnormally. Eight died by jumping off buildings, running into traffic or other rash action.
Japan, the largest importer of Tamiflu, has suspended the drug from being administered to teenagers while studying any link between the medicine and the erratic behaviour.
A health ministry panel could not prove the connection by the time it reported the interim results to the government on Tuesday, but the ministry said it would keep its precautionary ban on the drug for teenagers.
"The panel will come to a conclusion after more studies," a health ministry official said. "This report is only something transient and we should not rush to any decision right now."
The panel will continue to study additional cases, with data to be collected until March, he said.
One of the working teams of the panel studied some 10,000 cases of flu patients 17 years old and younger, of whom about 80 percent had taken Tamiflu.
After studying the cases provisionally, the team found the risk of erratic behaviour was greater among the patients who did not take the drug than those who did, the ministry said.
Specifically, 14.7 percent of the total showed some abnormal behaviour including minor symptoms, such as saying something strange. Of them, only 3.2 percent acted dangerously such as jumping off buildings, the ministry said.
Another working team said nearly 40 percent of patients who acted abnormally had not taken the drug and warned that all flu patients could show erratic behaviour.
An investigation last year by the US Food and Drug Administration into the deaths in Japan concluded there was no link with Tamiflu.
Swiss drugmaker Roche, the manufacturer of Tamiflu, has repeatedly denied any connection between the drug and the incidents.